1. BENTHIC MACROINVERTEBRATE IDENTIFICATION
TROUT UNLIMITED
COLDWATER CONSERVATION CORPS

2. THE CCC BMI PROCESS Select sampling site and specific locations.
Obtain sample(s).
Sort and identify critters to Order (Family, in a few cases).
Count number of organisms in each Order and enter data in the CCC Macroinvertebrate Count Data Sheet.
Enter group data into the water quality rating algorithm and compute water quality rating (i.e., biological index).

3. TAXONOMIC SEQUENCE Example Animalia Kingdom Arthropoda Phylum Insecta
Plecoptera (Stoneflies)
Capniidae (Winter Stoneflies)
Capnia
vernalis (Early Black Stonefly)
Kingdom
Phylum
Class
Order
Family
Genus
Species
Slide shows the taxonomic classification of the early black stonefly, Capnia vernalis.
Taxonomists have added to this sequence with superorder, superfamilies, subfamilies, etc. Not important for our purposes, and we’ll ignore them.
We will be identifying organisms to Order, and in some cases, Family. That is sufficient to compute a biological index value, providing a numerical characterization of the benthic community.

4. POLLUTION TOLERANCE
We will group our critters into three categories of pollution tolerance.
Sensitive to pollution
Somewhat sensitive
Pollution tolerant

5. POLLUTION SENSITIVE TAXA
Stonefly Nymphs [Order Plecoptera]
Mayfly Nymphs [Order Ephemeroptera]
Non-Net Spinning Caddisfly Larvae (case builders) [Order Tricoptera] and Free-living Caddisly Larvae
Hellgrammites (Dobsonfly Larvae) [Order Megaloptera]
Water Pennies (a beetle larva) [Order Coleoptera]
Riffle Beetle Adults [Order Coleoptera]
Gilled Snails [Class Gastropoda]
These are organisms that are highly sensitive to pollution. Any appreciable amount of pollution, and they will be reduced in the benthic community, or disappear completely.
Stonefly nymphs require clean, cold, well-oxygenated water. Their presence in the benthic community tells us a lot about water quality. In fact, there are those who feel that, once you have established the presence of stoneflies in the benthic community, you need look no further.
Mayflies are one of the most common and important members of the freshwater bottom-dwelling community – over 700 species in North America. If you are a fly fisherman, you are certainly aware of their importance. They occur in a wide range of stream habitats, from the Baetis nymphs of rocky riffles to the Green Drake nymphs in soft sediments.
Caddisflies are a large and important group of aquatic insects – over 1200 species in North America. Non-net spinning caddisflies include case builders and free-living (Rhyacophila) species.
If you grew up bass fishing, you certainly know what hellgrammites are. They are one of the largest insect larvae you’ll encounter.
Water Pennies are the larvae of a beetle; adults are terrestrial.
Riffle beetles are one of the few beetles that reside in the benthic zone as adults.
There are two major groups of snails – Those with gills, and those having lungs. Snails having gills are sensitive to pollution.

6. SOMEWHAT SENSITIVE TAXA
Cranefly Larvae [Order Diptera – Family Tipulidae]
Net-Spinning Caddisfly Larvae [Order Tricoptera – Families Hydropsychidae, Philopotamidae, Polycentropodidae]
Dragonfly Nymphs [Order Odonata]
Damselfly Nymphs [Order Odonata]
Scuds [Order Amphipoda]
Sowbugs [Order Isopoda]
Cranefly adults look like giant mosquitos.
The larvae of these three families of caddisfly use nets to capture food.
The Order Odonota is divided into two major groups – Dragonflies and Damselflies. Their larvae are aquatic; most species are predaceous.
Scuds and sowbugs are more common in limestone streams and tailwaters, but can be found in freestone streams.

7. SOMEWHAT SENSITIVE TAXA (cont.)
Beetle Larvae [Order Coeoptera]
Fishfly Larvae [Order Megaloptera – Family Corydalidae]
Alderfly Larvae [Order Megaloptera – Family Sialidae]
Crayfish [Order Decapoda]
Clams [Class Pelecypoda]
Continuing with groups somewhat sensitive to pollution
There are over 30,000 known species of beetles in North America. Of those, 1,000 or so are aquatic or semi-aquatic. However, the larvae of water beetles remain poorly known.
Fishflies are in the same Order as the hellgrammites (dobsonflies) and are very similar in appearance. Fishfly larvae are much smaller, however, up to an inch long.
Alderflies are related to fishflies and dobsonflies – same Order, but different families. As we’ll see, it is easy to differentiate alderflies.

8. POLLUTION TOLERANT TAXA
Midge Larvae [Order Diptera – Family Chironomidae]
Blackfly Larvae [Order Diptera – Family Simulidae]
Aquatic Worms [Class Oligochaeta]
Leeches [Order Hirudinea]
Other Snails [Class Gastropoda]
If you fly fish, you know about midges, both larvae and adults. If you are like me, you’re reluctant to fish them because they’re so friggin’ small.
Blackflies are another member of the Order Diptera – true flies. As you’ll see the larvae are pretty easy to identify.
Aquatic worms are segmented. They are most often imitated with the San Juan worm pattern.

9. Identification Notes Aquatic Insect Body Plan
Head
Thorax
Abdomen
Thoracic segments – 3
Legs – 3 pairs (on thoracic segments)
Abdominal segments - variable

10. Identification Notes Mayflies (Ephemeroptera)
Cylindrical to flattened form
Slender antennae
Platelike or feathery gills on abdomen
Single tarsal claw at end of middle and hind legs
Most species have three tails, but some have only two.

11. Identification Notes Stoneflies (Plecoptera)
Long, slender antennae
Wing cases prominent on thorax
Gills on thorax
Two tails

12. Identification Notes Cranefly Larvae (Tipulidae)SS
Identification Notes Cranefly Larvae (Tipulidae)
Wormlike; segmented
No legs
Tentacles or fleshy lobes at tip of abdomen
Head usually with-drawn into thorax; they often appear headless
If you’ve tied a Walt’s worm, you tied a cranefly larva imitation.

13. Identification Notes Blackfly Larvae (Simuliidae)
Single proleg located ventrally behind head
Posterior of abdomen enlarged – body appears club-shaped
Gills at posterior end of body
Well-defined head; not withdrawn.

14. Identification Notes Midge Larvae (Chironomidae)
Small; segmented; usually red or greenish
Well-defined head
Paired prolegs immediately behind the head
Paired prolegs on terminal segment; also (usually) short projections w/tufts of hairs

15. Identification Notes Dragonfly Nymphs (Odonata)SS
Identification Notes Dragonfly Nymphs (Odonata)
Large eyes
Wicked mandibles (jaws)
Wide abdomen
Breathe thru their anus!

16. Identification Notes Damselfly Nymphs (Odonata)SS
Identification Notes Damselfly Nymphs (Odonata)
Elongate, slender form
Two sets of wing pads
Three feathery gills on end of abdomen

17. Identification Notes Scuds (Class Amphipoda)
Look like little shrimp
Body flattened from side to side
Two pairs of long antennae
Seven pairs of legs

18. Identification Notes Sow Bugs (Class Isopoda)
Segmented body; last segment larger than the rest
Two pairs of antennae – one short, one long
Seven pairs of legs – last pair look like flattened tails

19. Identification Notes Water Penny (Coleoptera)
Larvae are flattened and disclike.
Easily recognized
Found attached to rocks
Water pennies are highly adapted for living in swift waters. They eat algae and other materials found on rocks.

20. Identification Notes Riffle Beetles (Coleoptera)
Smaller than most other beetles
Antennae usually slender, but sometimes clubbed
Claws at ends of legs
“Clubbed” means that the antennae have an enlarged section at the end. Antennae may look like a baseball bat or a club. May be hard to discern with a hand magnifier.

21. Identification Notes Dobsonfly Larva (Megaloptera)
Large critters; 1 to 6.5 inches
Filaments on each abdominal segment
Two anal prolegs with hooks
Well developed chewing mouthparts (see next slide)
Legs
Better known as hellgrammites.
Filament

22. Identification Notes Dobsonfly Larva (Megaloptera)SS
Identification Notes Dobsonfly Larva (Megaloptera)

23. Identification Notes Fishfly Larva (Megaloptera)SS
Identification Notes Fishfly Larva (Megaloptera)
Smaller than dobson-fly (hellarammite) larva; ½ to 1 inch.
Reddish-tan; sometimes with yellow streaks
Filaments on abdominal segments
Two anal prolegs with hooks
Look very much like hellgrammites, but much smaller.

24. Identification Notes Alderfly Larva (Megaloptera)SS
Identification Notes Alderfly Larva (Megaloptera)
Smaller than dobson-fly (hellagrammite) larva; ½ to 1 inch.
Lateral filaments on abdomen have 4-5 segments.
A single terminal filament
Dobsonfly and fishfly larvae do not have that terminal filament.

25. Caddisflies (Trichoptera)
A large group of aquatic insects – over 1,200 species
Larvae are often a large and important component of benthic communities
Sensitive: a number of families of case-building caddisflies and the free-living caddisflies of Family Rhyacophilidae
Somewhat sensitive: the net-spinning caddisflies of Families Hydropsychidae, Philopotamidae, and Polycentropodidae

26. Identification Notes Caddisflies - Rhyacophilidae
Free-living; do not build cases or spin net for feeding
A single dorsal plate behind the head (1st thoracic segment)
Two prolegs with single claws on last (9th) abdominal segment.

27. Identification Notes Caddisflies - Rhyacophilidae
Green rock worm (Genus Rhyacophila)
Note single dorsal plate on first thoracic segment and anal prolegs
These are free-living caddisfly larvae. Most species are active predators. Most of the 100 or so species in North America belong to genus Rhyacophila. They are predominantly green in color. Larvae are found primarily in clear, cold streams, making this an important benthic macroinvertebrate in trout streams. Very abundant in Pine Creek, north of Pittsburgh.

28. Identification Notes Caddisflies – Case Builders
Pull a caddisfly larva from its case to verify that the uncased larvae you see are not just case-building types that have left their cases.

29. Identification Notes Caddisflies – Case Builders

30. Identification Notes Caddisflies - HydropsychidaeSS
Identification Notes Caddisflies - Hydropsychidae
Body typically curved
Dorsal plates on all three thoracic segments
Anal prolegs usually have a tuft of long hairs.

31. Identification Notes Caddisflies - PhilopotamidaeSS
Identification Notes Caddisflies - Philopotamidae
Body typically curved
Dorsal plate on only the first thoracic segment
No gills on abdomen
Labrum (upper lip) modified to form a scraper.
Upper lip is modified for scraping algae and other material off the rocks. Upper lip looks like the end of your ice scraper for your car windshield.

32. Identification Notes Caddisflies - PolycentropodidaeSS
Identification Notes Caddisflies - Polycentropodidae
Dorsal plate on only the first thoracic segment.
Abdominal segments with some short hairs, but no gills
Trochantin (shoulder blade) sharply pointed.

33. Identification Notes Gilled Snails – (Gastropoda)
Spiral shaped
Opening is on the right
A thin horny plate (the operculum) covers the opening when the foot is retracted

34. Identification Notes Other Snails – (Gastropoda)
Can be spiral shaped or coiled
Do not have an operculum
If spiral shaped, opening is on the left
Because their shells are constructed of calcium carbonate, snails are not common in most freestone streams, especially in non-glaciated areas (the same is true of clams and mussels). You typically find them in slower water, often attached to vegetation. Generally not found in faster water.

35. Identification Notes Beetle Larvae (Coleoptera)SS
Identification Notes Beetle Larvae (Coleoptera)
Distinct head with chewing mouthparts
Thoracic legs usually present
Eight to 10 abdominal segments
Never have terminal prolegs
Photo: Predaceous diving beetle larva
There are 112 families of beetles, but only about 10 are truly aquatic. Unfortunately, beetle larvae do not have any distinct distinguishing feature. You may arrive at identification of a specimen as a beetle larva by process of elimination. I can’t be of much help here, but we’ll continue to work on better guidance for you.

36. Identification Notes Beetle Larvae (Coleoptera)SS
Identification Notes Beetle Larvae (Coleoptera)
Left: larva of a water scavenger beetle; notice well-developed mouthparts (tearing and shredding).
Right:

37. Identification Notes Beetle Larvae (Coleoptera)SS
Left: Whirligig beetle larva
Right: Riffle beetle larva

38. Useful References How to Know the Aquatic Insects (Spiral-bound)
by Dennis M. Lehmkuhl
Good drawings and identification keys to Order, and in some cases Family.
Available used (good or very good condition) via Amazon.com for under $20 ($61 new).
A Guide to Common Freshwater Invertebrates of North America by J. Reese Voshell, Jr.
Available new via Amazon.com (~$25); also available used

39. Useful References
Aquatic Entomology – The Fishermen’s and Ecologists’ Guide to Insects and Their Relatives by W. Patrick McCafferty
Available new and used via Amazon.com (variable pricing)

40. Helpful Web Links
Freshwater Macroinvertebrates of New York.
Bugguide.net. Great photos and information! Can search by order, class, etc.
IOWATER Photographic Guide to BMI. Great photos; geared toward volunteers.
IOWATER guide is 16 MB pdf file.